1. Field of the Invention
The present invention relates to a power supply, and more particularly, to a power supply having a function of a power saving mode.
2. Description of the Prior Art
As shown in FIG. 1, a conventional SMPS (switching modulation power supply) has an input unit 1 including F, L G, and N terminals, a rectification unit 2, a switching unit 3 including IS, FB, RT, CT, OUT, and CS terminals, a feedback unit 4, and an output unit 5.
External AC power is supplied through the input unit 1, and the input AC power is converted into DC power by a bridge diode in the rectification unit 2. The rectified power is supplied to the output unit 5, through a transformer in response to an operation of the switching unit 3.
The feedback unit 4 detects a ripple in a reference voltage (+5V) output by the transformer, and feeds back the increase and the decrease of ripple to a feedback terminal FB of a Pulse Width Modulator-Integrated Circuit (PWM-IC) 31 through photo couplers PC1-1 and PC1-2 and an associated photo transistor.
The PWM-IC 31 maintains an output voltage as a constant voltage by controlling the power output to the output unit 5 through PWM (pulse width modulation) based on the feedback signal from the output unit 5.
The output unit 5, illustrated in FIG. 1 includes a power supply terminal 51 for supplying input power input to an electronic product, and a general ground terminal 52, shown in FIG. 2. Where the output unit 5 is connected to the electronic product, the electronic product is operated by using a predetermined power output from the power supply terminal 51 of the output unit 5 as an operational power.
Where the power supply is used, the power supply is connected and disconnected to and from the electronic product in a state where external power is being supplied to the power supply.
For example, where the power supply is disconnected from the electronic product, there is are risks of damage to internal elements of the power supply and consumption of unnecessary power due to unnecessary operation of the power supply because the external power is constantly being supplied to the power supply.
Moreover, there is another risk of damage of the electronic product and the power supply due to a peak electric current and voltage such as the spike voltage T shown in region R of FIG. 3. Where the power supply is connected to the electronic product while the power supply is being supplied with the external power, the peak electric current and voltage are generated. That is, the spike is generated by an inrush current to the electronic product. The inrush current occurs due to suddenly connecting the electronic product to the power supply while the output of the power supply is available.
Therefore, the conventional power supply has a risk of damage and consumption of unnecessary power over a long period of time.